jim wrote:
On 19 Dec, 16:21, "Bob Eager" wrote:
On Fri, 19 Dec 2008 15:41:51 UTC, wrote:

ISTR hearing that the story began with experiments on immersion
heaters and was erroneously extrapolated to central heating which is,
of course, completely different.

It's not valid for them anyway.

You have something which, left to its own devices, loses heat over time.
The rate of heat loss will reduce as its temperature gets nearer to that
of its surroundings (heat transfer rate depends on difference in
temperature).

If left to cool, there is reducing heat loss over whatever time elapses.
If kept at same temperature, there is heat loss over the same time, but
it's constant (-ish) because the temperature difference does not reduce
- i.e. more heat is lost over the same time.

In both cases, that heat loss has to be made up. That's how much
fuel/cost will be involved. More heat lost - more cost.

ISTR there was some point about older (solid wall) houses that fair
worse if unheated for periods as the walls get damp from rain etc and
so become even worse at insulating until they are dried out again -
which takes more heat than if they were kept up to temp (and losing
heat) throughout same period - even so still seems a bit
"mathematical" to me to be relied on.....

Jim

But switching the heating off overnight doesnt see a house lose much
temperature. To get the effect you mention it would need to be off a
month or more.


NT